Roof Vent Square Footage

In cases where a roof has a complex shape such as in the image to the right measuring the dimensions and areas of each part of the roof to calculate total area will result in a more accurate measurement of area.

Roof vent square footage.

Divide this by 144 to calculate how many square feet each vent is. One square foot equals 144 square inches so the standard 16 inch by 8 inch soffit vent is 0 89 square feet. Attic square footage 2 square inches of exhaust and square inches of intake net free area nfa needed. Ventsure 4 foot strip heat moisture ridge vent.

6 measure the radius of round vents or take half the diameter of the. Federal housing authority recommends a minimum of at least 1 square foot of attic ventilation evenly split between intake and exhaust for every 300 square feet of attic floor space. 1 500 square feet 300 5 square feet. 27 lineal feet required.

For example a 6 by 12 inch soffit vent has 72 square inches which when divided by 144 results in a 0 5 square foot opening. There are also gable and roof fans which actively pull the hot air out of the attic. Choose one of the following products to meet the recommended exhaust nfva of 528 square inches. Thus if your attic is 450 square feet you need roof vents equaling 3 square feet.

For example if you use 16 inch by 8 inch soffit vents each vent is 128 square inches. The calculator cannot account for complex shapes based on a measurement of square footage alone. We know we need 5 square feet total of ventilation area. Flat roof vents have no moving parts to break or squeak but don t vent as much air as wind driven vents.

See how simple that was. Calculate or enter the square footage of the attic or area to be vented. Ventilation manufacturers assign an nfa value to the non motorized vents they make. Based upon just about everyone s recommendations 60 percent or 3 square feet of this should be in the soffit area and the remaining 40 percent 2 square feet should be located at the ridge of the roof.

As a general rule your roof needs 1 square foot of vent area for every 150 square feet of attic space. If there is no vapor barrier double it to one square foot of nfa for every 150 square feet of attic floor space half for intake half for exhaust. Pick out your soffit vent size and determine the square footage of the vent. If your attic floor has a vapor barrier you will need one square foot of nfa per every 300 square feet of attic floor area half of that will be intake half for exhaust.